As you may know some months have 31 days a year and others have 30. And one has 28 or 29 days.
In some contexts, for instance interest calculation it is not uncommon to apply a method like 30/360, which means that you assume all months are
30 days, and that there are only 360 days a year. (Essentially this means that the 31st of all months is free of interest. And 28 Feb counts as three days.)
We don't know your context, and you original post only asked for going back 64 years and 6 months. But since you indicated an expected result, a better query might be: